Project Summary/Abstract The gut microbiome is composed of a diverse and dynamic community of microorganisms in the intestinal tract. Using germ-free model organisms, recent research has established the importance of these communities in performing key metabolic, endocrine, and immunologic processes in the host. The majority of this research has focused on the microbiome's effects on the intestine, the tissue with which it is in the most intimate contact. Recent studies, however, have revealed that these effects are significantly more far-reaching, with roles in hepatic, cardiovascular, and even neurological health. As the primary metabolic and detoxification hub, the liver is a critical checkpoint between the digestive functions of the gut and the rest of the body. Therefore, it is likely that alterations in the gut microbiota affect liver health and homeostasis. We utilized germ-free and microbiome-replete mice to investigate the effects of the gut microbiome on liver metabolism. Analysis of preliminary metabolomics data suggests significant alterations in hepatic metabolism, most notably in the antioxidant and xenobiotic detoxification pathways classically controlled by the transcription factor Nrf2. Activation of Nrf2 and its downstream pathways are cytoprotective against an array of oxidative liver insults, including drug-induced liver injuries such as acetaminophen-induced hepatotoxicity. To extend these findings beyond the artificial germ-free system, we propose to investigate the effect of microbiome manipulation on the activation and functionality of these critical detoxification pathways. Our group has previously shown that the widely studied probiotic Lactobacillus rhamnosus GG (LGG) can mediate protective effects in the intestine through activation of the Nrf2 pathway. Based on these observations, we hypothesize that LGG induces Nrf2 signaling in the liver and that this is protective against oxidative liver injury. The specific aims of this proposal are 1) to determine the extent of Nrf2 activation in the liver in response to LGG administration and 2) to identify the effect of oral LGG administration on the pathogenesis of oxidative liver injury using a mouse model of acetaminophen-induced hepatotoxicity. The long-term goal of this research is to understand the mechanisms by which probiotics and the microbiome contribute to host homeostasis and disease.